1. Field of the Invention
The present invention relates to polarizing elements and to the manufacture and use thereof. Some preferred embodiments relate to short-wavelength polarizing elements, to methods of manufacturing such polarizing elements, to methods of evaluating exposure apparatuses using such polarizing elements, and/or to methods of manufacturing semiconductor devices using such exposure apparatuses.
2. Description of the Background
In the related art, exposure apparatuses have been widely used to expose circuit patterns for liquid crystal displays or semiconductor devices. Typically, the exposure apparatus performs a so-called lithography process, in which an original pattern formed on a photomask is reduced and transferred to the substrate. With requirements for smaller features in semiconductor devices, shorter-wavelength light sources and larger-diameter projection optical systems have been promoted to achieve higher lithographic resolution. An exposure apparatus with a numerical aperture (NA) of 0.9 or more using an ArF excimer laser (e.g., 193 nm wavelength) is currently entering the practical application stage. In addition, an ArF immersion-type exposure apparatus has been developed, wherein liquid fills the space between the lowest lens of the projection optical system and the substrate; this apparatus can provide an air-equivalent NA of 1.0 or more. An exposure apparatus has also been developed which uses an F2 excimer laser (e.g., 157 nm wavelength). In addition, an F2 immersion-type exposure apparatus has also been discussed.
Although polarization has not been a significant concern in conventional exposure apparatuses, in such larger-diameter exposure apparatuses, polarization of the light is an important factor. Notably, conventional exposure apparatuses often convert the light from the laser source into an unpolarized state before illuminating the mask. Unpolarized light comprises s-polarized and p-polarized components of equal magnitude; the p-polarized component decreases the image contrast in a larger-diameter exposure apparatus. Therefore, prior to projection, the exposure apparatus needs to reduce the p-polarized component; in the limit where only the s-polarized light remains, tangential linear polarization is obtained, though this limit need not be reached for the lithographic resolution to be enhanced.
An optical element called a polarizer, or polarizing element, is used to control the polarization state. Polarizers can be divided into prism-type and filter-type elements. Prism-type polarizers use the birefringence of optically transmissive crystals such as calcite, or Brewster-angle reflection, or the like. Prism-type elements can yield a high degree of polarization, as gauged by the extinction of light transmitted through two such polarizers in a crossed configuration. However, prism-type elements produce a substantial deflection between the incoming and outgoing light rays. Moreover, they are relatively thick which, thus, requires a larger installation space within the exposure apparatus. Moreover, they have a small viewing angle.
While filter-type polarizers generally have poorer polarization characteristics than prism-type polarizers, they have the important advantages in that they can be formed as thin devices, requiring a smaller installation space within an exposure apparatus and in that normally-incident light can be polarized with no deflection of the beam. Furthermore, they have a larger viewing angle and can effectively polarize obliquely-incident light. By way of example, a filter-type polarizer for visible light can be formed by rolling in one direction a glass mixed with conductive particles such as silver halide, thereby forming the silver halide particles into an elongated shape. These elongated silver halide particles produce an anisotropic electric conductivity that imparts the polarization characteristics to the composite material. However, such polarizers are ineffective for ultraviolet (UV) light because materials which are transparent to UV light, such as fluorite or fluorine-doped amorphous quartz or the like, cannot be rolled to produce orientation of embedded particles.
Another well-known filter-type polarizing element is a wire grid polarizer (WGP). Typically, a WGP includes a glass substrate on which thin parallel lines of a metal, such as aluminum or gold, are equally spaced. The WGP possesses anisotropic electric conductivity, as in the above-described polarization filter. The WGP needs to have the thin metal lines located at an interval sufficiently smaller than the wavelength of the light to alter its polarization. Thus, WGPs are currently employed only at infrared wavelengths and longer due to the limits of conventional machining.
It has been reported that electron beam lithography can produce a WGP with a period of approximately 200 nm, which can effect polarization of visible light. See U.S. Pat. No. 6,108,131 incorporated herein by reference in its entirety. It has also been reported that a 50 nm half pitch (100 nm interval) WGP was fabricated by nanoimprint lithography that polarizes the light at 450 nm wavelength. See She-Won Ahn, et al., Nanotechnology, Institute of Physics Publishing, Vol. 16 (2005), pp. 1874-1877, incorporated herein by reference in its entirety. However, such a WGP cannot polarize light in the deep-UV region (e.g., with a wavelength of about 200 nm or less).
To polarize the light from an ArF excimer laser (e.g., 193 nm wavelength) or an F2 excimer laser (e.g., 157 nm wavelength) with a WGP, the metal lines would need to be spaced at an interval of 50 nm or less, which was unachievable with current electron-beam machining technology. While a variety of systems and methods are known, there remains a need for improved systems and methods that can overcome the foregoing and other deficiencies of existing systems.